Beam modulating devices and method



G. w. PRESTON 3,023,342

BEAM MODULATING DEVICES AND METHOD Feb. 27, 1962 Filed July 18, 1958 2Sheets-Sheet 1.

INVENTOR. A G'ZE/V/V w EPA-J70 1962 e. w. PRESTON 3,023,342

BEAM MODULATING DEVICES AND METHOD Filed July 18. 1958 2 Sheets-Sheet 2JNVENfbR. "f GLW/l 14 Ream/v- BY Wigwam United States Patent C 3,023,342BEAM MODULATING DEVICES AND METHOD Glenn W. Preston, Oreland, Pa.,assignor to General Atronics Corporation, Bala-Cynwyd, Pa., acorporation of Pennsylvania Filed July 18, 1958, Ser. No. 749,555 7Claims. (Cl. 315-12) The invention relates to particle selecting devicesand method, and more particularly devices and method for modulating abeam of electrically charged particles.

Heretofore, beam modulating devices have been provided having the formof an electron gun which have varied the intensity of a beam ofelectrons. However, such modulation has also varied the point of focusfor the electrons and the forms of the devices have tended to reduce thelife of their electron emitting cathodes.

It is, therefore, a principal object of the invention to provide a newand improved device and method for controllably selecting chargedparticles without substantially varying the paths of the unselectedparticles.

Another object of the invention is to provide a new and improved deviceand method for modulating a beam of charged particles withoutsubstantially affecting their point of focus. i

Another object of the invention is to provide a new and improved beammodulating device and method providing negative spherical aberration ofits beam which may compensate for positive spherical aberration of thebeam.

Another object of the invention is to provide a new and improved beammodulating device and method requiring low signal power and voltage formodulating the intensity of its beam of electrons.

Another object of the invention is to provide a new and improved deviceand method for modulating a beam of charged particles which providesoptical properties of its beam which are substantially independent ofthe total beam current.

Another object of the invention is to provide an electron device formodulating a beam of charged particles which has a low input capacitanceto its beam modulating control electrode.

Another object of the invention is to provide a new and improved beammodulating device providing uniform cathode loading of its electron gun.

Another object of the invention is to provide a new and improved beammodulating device having high transductance.

Another object of the invention is to provide a new and improved beammodulating device responsive to high frequency modulating signals andhaving good insulation between input electrodes.

Another object of the invention is to provide a beam modulating deviceand method which may readily be adapted for many varied uses.

Another object of the invention is to provide a new and improved beammodulating device and method which is highly efiicient in operation,provides low heat loss in its modulating operation, and has a highcurrent and power capacity.

Another object of the invention is to provide a new and improved beammodulating device which may be readily utilized as an amplifier, acathode ray tube, a klystron, and a signal combining means, inappropriately modified forms, having all the advantages stated above.

The above objects of the invention as well as the many other objects areattained by providing a beam modulating device comprising a plate memberfor absorbing and reflecting incident charged particles of a beam, andguide means for directing particles of the beam towards the platemember. The plate member is provided with a connection for having itspotential controlled to regulate its absorbing and reflecting action formodulating the amplitude of the beam of particles produced by thedevice. The guide means is in the form of a magnetic field for directingincident particles towards and reflected particles from the plate memberalong different non-reciprocal paths.

The charged particles may be negatively charged electrons in the form ofa beam derived from the cathode of an electron gun. An apertured elementwhich electrically shields the plate member is interposed between thesource of electrons and the plate member, while the magnetic field ofthe guide means deflects the beam of electrons through the aperture ofthe element so that the beam path is substantially perpendicular to thesurface of the plate member when proximate the plate member. With thepotential between the plate member and the element controlled to providean electric field for regulating the ratio of absorption to reflectionof electrons by the plate member, the electrons reflected by the platemember form a beam which is deflected by the magnetic field of the guidemeans through the aperture of the element and into a non-reciprocalundeflected path forming a predetermined angle with the'undeflected pathof the beam of electrons from the source.

The method as applied to a beam of negatively charged electron particlescomprises subjecting the particles of said beam to a magnetic field fordirecting the particles along the path into an electric field parallelto the direction of the electric vector, varying the amplitude andpolarity of the electric field for controlling the proportions ofelectrons rejected by the electric field back into the magnetic field,and utilizing said magnetic field for forming a beam of the rejectedelectrons along a path in a predetermined direction.

The foregoing and other objects of the invention will become moreapparent as the following detailed description of the invention is readin conjunction with the drawings, in which:

FIGURE 1 is a side elevational view with portions broken away of acathode ray tube embodying the invention,

FIGURE 2 is a side elevational view with portions broken away of anamplifier tube embodying the invention,

FIGURE 3 is a sectional view taken on line 33 of FIGURE 2,

FIGURE 4 is a side elevational view of a signal combining meansembodying the invention,

FIGURE 5 is a partially diagrammatic view taken on the line 5-5 ofFIGURE 4, and

FIGURE 6 is a diagrammatic representation of a klystron embodying theinvention.

Like numerals designate like parts throughout the several views.

Refer to FIGURE 1 which discloses a cathode ray tube 10 embodying theinvention. The cathode ray tube 10 has a glaSS envelope 12 with a firstportion 14 of circular cross section having its end connected to a base16 with connecting pins 18, and a second portion 20 of circular crosssection. The first and second portions 14, 20 are joined with their axesat an angle of degrees and forming an intermediate cylindrical portion22 symmetrically arranged with its axis at an angle of degrees with eachof the axes of the first and second portions 14, 20 of the envelope 12.The envelope 12 is also provided with a conical enlarged portion 24 atthe end of the portion 20 and has a substantially flat face areaportion-26. The tube It) has its cavity within the envelope 12 evacuatedin the usual manner, and is sealed.

The first portion 14 of the envelope 12 contains an electron gun 28 forproducing a beam 30 of electrons of subwards the intermediate cylinder22.

It is noted, that the electron gun 28in this case, may be designed witha slightly diverging electric field at its emitting surface for insuringincreased life and dependability, whereas the field is usuallyconverging, overloading the central portion of the cathode, in prior artbeam modulating devices.

When the electrons of the beam enter the region 34 of the cylinder 22,they are deflected to the left along a curved path 36 by the fieldproduced by the electric coil 38 positioned on the outside of thecylinder 22 about the region 34 and proximate to the first and secondportions 14, 20 of the envelope 12.

After being deflected, the beam 30 of electrons proceeds along a path 40through an aperture 42 in a shielding element 44 and towards a platemember 46.

The shielding element 44 has the form of a cylindrical body with a wall48 and a plane base portion 50 having the aperture 42 at its center. Theshielding element 44 is maintained in position within the cylinder 22 byspring adjusting means 52. In this manner, the base 50 of the element 44is interposed along the path 40 of the beam 30 of electrons between themagnetic field in the region 34 and the plate member 46. The shieldingelement 44 is made of electrically conducting material which is perviousto magnetic lines of flux.

The plate member 46 is secured within the cylinder 22 at its bottom 54in parallel spaced relation to the base 50 of the shielding element 44.The shielding element 44 is connected to a lead 56 which, for example,may receive a positive potential of about 400 to 4000 volts with respectto the cathode of the electron gun 28. The plate member 46 is connectedto a lead 58 which may be maintained at substantially cathode potentialand varied positively and negatively by a modulating voltage signal. Inthis connection, the magnetic field produced by the coil 38, forexample, may be in the order of 100 to 500 gausses to provide therequired deflection for the beam. The change in intensity of theelectric field between the shielding element 44 and plate member 46produced by the modulating voltage signal on lead 58 is effectivelyshielded by the element 44 from the other regions within the envelope 12of the cathode ray tube 10.

- As the beam of electrodes proceed toward the member 46 along the path40 through the aperture 42 of the element 44, they enter the region 60of the electric field between the shielding element 44 and the platemember 46. The lines of force of the electric field produced by thisconfiguration are substantially parallel and perpendicular to the platemember 46. The electrons of the beam upon entering the region 60 areaccelerated or decelerated in accordance with the polarity of theelectric field.

In operation, the polarity of the electric field is adjusted to retardand decelerate the incident electrons in their motion towards theintercepting surface 62 of the plate member. 7 It is also noted that thepath 40 of the beam of electrons is substantially parallel to theelectric field vector so that there is no component of lateralacceleration or velocity and the path 40 is substantially perpendicularto the intercepting surface 62 of the plate member 46. If the voltage onthe plate member 46 is sufliciently above cathode potential, most of theelectrons in the path 40 will reach the plate member 46 and be absorbed.However, as the potential of the plate member 46 is reduced a decreasingnumber of electrons will reach the plate member 46, while the remainingelectrons will have their velocity reversed before they reach the platemember 46 and be rejected from the region 60 along a path 64 coincidentwith the path 40. The electrons will move along the path 64 through theaperture 42 and into the region 34 of the magnetic field produced by thecoil 38. At this time, since the direction of the electrons along theirpath 64 is reversed from that along the path 40, the magnetic fielddeflects the electrons along a non-reciprocal curved path 66 into theundeflected path 68. The rejected electrons form a beam 70 along thepath 68 proceeding axially along the portion 20 of the envelope 12towards the enlarged end portion 24.

It is noted that the boundaries of the magnetic field in the region 34transversed by the electrons of the beam 30 are substantially plane andparallel to the intercepting surface of the plate member 46 and orientedat an angle of substantially 45 degrees to the direction of theundeflected beams 30 and 68. This angle of the boundary of the magneticfield within the region 34 acts to broaden the beam 30 as it enters themagnetic field. This is due to the fact that the electrons in the beamto the left are acted upon earlier than the electrons to their rightalong the cross section of the beam. The broadening of the beam servesto decrease the electron density of the beam, and thereby, increase theefiiciency of the'reflecting operation of the device. It is noted that,since the beam is doubled back upon itself along the paths 40, 64, thistends to maintain the beam density at a value substantially equal tothat of the beam along the path 32.

As the beam is deflected along path 66 and leaves the magnetic field inthe region 34 it is directed into a path 68 which is also at an angle ofsubstantially of 45 degrees with the boundary of the magnetic field.This has the effect of sharpening or narrowing the beam and increasingits density to a value that is substantially the same as that of thebeam 30 along the path 32 when the beam is unmodulated. As previouslynoted, however, the beam 70' may have introduced therein negativespherical aberration due to the reflecting process undergone by itselectrons.

The proportion of electrons absorbed to those rejected or reflected is afunction of the potential of the plate member 46. Therefore, as themodulating signal varies the voltage on the plate member 46 theintensity of the beam 70 formed of reflected electrons varies in acorresponding manner. Since the incident electrons move perpendicular tothe intercepting surface 62 of the plate member 46 the electrons whichimpinge upon and are absorbed by the member 46 have lost most of theirenergy, thereby minimizing the heat produced in the member 46, and theenergy and power required to operate the device. It is also noted thatthe electrons which are reflected or repelled by the electric field 60do not lose any of their energy, which is regained by their passage inthe opposite direction through the electric field in the region 60.

Since this device does not utilize the grids commonly used in electrondevices, the partition noise resulting therefrom is eliminated, therebyincreasing the signal to noise ratio obtainable. This structure alsoprovides a high transconductance for the tube 10 as well as a lowcapacitance to the input lead 58 of the plate control member 46receiving the beam modulating signal, because of the relatively largeseparation between the base 50 and the plate member 46.

The modulating device also provides an electron beam 70 which, whilehaving its amplitude modulated, does not vary its focal point. Thereflecting method of the structure also provides a negative sphericalaberration which may compensate for the positive spherical aberrationusually present due to the focusing and other means of the cathode raytube 10. The optical properties of the beam are, thus, independent ofthe total current of the beam. This is a very highly desirable property.

As the beam 70 of electrons proceeds along its path 68,

itpasses through an aperture 72 in the transverse wall portion 74 of afocusing cylinder 76 positioned within the portion 20 of the envelope12. The beam 70 passes through the focusing cylinder 76 and between thehorizontal and vertical deflecting plates '78, 80. The deflecting plates78, 80 provide for horizontal and vertical deflection of the beam 70which proceeds towards the face portion 26 of the cathode ray tube 10and impinges upon its electron collecting surface.

In summary, the tube 10 produces a beam of electrons 108 of theshielding element 102.

30, preferably by providing a diverging electric field at the emittingsurface of the cathode. The beam 30 proceeds towards the region 34 ofthe cylinder 22, where it is broadened at the boundary of the magneticfield of coil 38 and deflected to the left along the circular path 36into path 40. The path 40 proceeds through the aperture 42 of theshielding element 44 into the electric field of the region 60. Dependingupon the potential difference and the resulting electric field producedby the plate member 46 and the shielding element 44, a greater orsmaller proportion of electrons will be absorbed by the plate 46, withthe remaining electrons being rejected or reflected back through theaperture 42 along the path 64. When the electrons move through themagnetic field in the region 34 they are deflected along thenonreciprocal circular path 66 into the path 68. The beam is narrowed atthe boundary as it emerges from the magnetic field. The electrons alongthe path 68 form a beam which is modulated in intensity and proceeds tothe right making an angle of 90 degrees with the beam of incidentelectrons along the path 32.

The electrons approach the plate member 46 substantially perpendicularto its intercepting surface 62, thereby, minimizing the energydissipated by the impinging electrons, While the reflected or rejectedelectrons regain their initial kinetic energy and are focused at thesame point, which is not dependent upon the beam intensity or themodulating signal. The shielding element 44 serves to shield themodulating electric field from the remaining portions of the envelope12.

The modulated beam 70 proceeds along the portion 20 of the envelope 12being focused by the cylinder 76 and deflected by the plates 78, 80 inthe usual manner. The negative spherical aberration produced by the beammodulating structure within the cylinder 22, compensates for andcounteracts the positive spherical aberration produced by the focusingcylinder 76.

Refer to FIGURES 2 and 3 which illustrate an electron tube 82 which is amodification of the device shown in FIGURE 1. The electron tube 82 has aglass envelope 84 providing an evacuated cavity. The left end portion 86of the envelope 84 has its end connected with a base 88 with pins 90. Acathode ray gun 92 is positioned within the end 86 of the envelope 84for producing a beam of electrons 94 which proceeds along an axial path96 towards the second end 98 of the envelope 84.

i The central portion 100 is provided with a cylindrical metallicshielding element 102 which is axially aligned with the axis of theenvelope 84'. A portion of the circular wall of the shielding element102 is deformed to provide a flattened region 104 having a centralaperture 106. The right end of the shielding element 102 is enclosed bya base. portion 108 having a central aperture 110.

The central portion 100 of the envelope 102 receives about it a magnet112 having poles 114, 116 providing a field therebetween shown withinthe dotted region 118 with lines of flux substantially parallel to theplane of the deformed portion 104 of the shielding element 102. Themagnetic ficldin the region 118 is symmetrically positioned on each sideof the aperture 106 with its flux lines perpendicular to the plane ofFIGURE 2.

A pair of magnetic coils 120, 122 are symmetrically positioned about theoutside of the envelope 12 at its central portion 100 on each side ofthe magnet 112 with their bottom ends 124, 126 spaced further apart thantheir top ends 125, 127. V p

Collecting plate 128 is positioned at the end of the portion 98 of theenvelope 84 in spaced relation to the base The collecting plate 128 isconnected with a lead 130 which may be returned to ground potentialthrough a load 132.

A plate member 134 is positioned outside the shielding element 102 inspaced relation to its deformed portion 104 and is connected externallyto a lead 136.

The tube device 82 operates in a manner similar to that of the device 10of FIGURE 1. A beam 94 formed of electrons emitted from the electron gun92 proceeds along the path 96 until it enters the magnetic fieldproduced by the magnetic coil in the region 138 within the envelope 84.

Since the beam 94 enters the magnetic field at its boundary at an anglediffering from 90 degrees, the beam is broadened. The electrons withinthe magnetic field, since their path is substantially perpendicular tothe lines of magnetic flux, are deflected along substantially circularpaths 140 and into substantially linear paths 142 as they emerge fromthe region 138. When the beam of electrons along the path 142 enter theregion 118 of magnetic flux produced by the magnet 112, they are againdeflected along substantially circular paths 144 and through theaperture 106 towards the intercepting surface of the plate member 134.

The beam of electrons, as it approaches the plate member 134, proceedsalong the path which is substantially perpendicular to the interceptingsurface of the member 134. The region 146 between the deformed portion104 of the shielding element 102 and the plate member 134 is providedwith a retarding electric'field of varying intensity controlled by therelative potentials of the shielding element 102 and the plate member134. As an example, the potential of the shielding element 102 may bemaintained at a positive voltage with respect to the cathode of theelectron gun 92 of about 20 to 400 volts for use of the tube device 82as an amplifier, while the plate member 134 may be maintained atsubstantially the same potential as the cathode of the electron gun 92and varied about this potential by a beam modulating signal delivered tothe terminal of a lead 136 for varying the intensity of the electronbeam reflected by the plate member 134.

As explained in connection with the tube device 10, the proportion ofthe reflected or rejected electrons, which are not absorbed by the platemember 134, is controlled by the potential signal delivered to the platemember 134. The reflected or repulsed electrons pass along a pathsubstantially perpendicular to and in a direction away from the platemember 134, through the aperture 106, then along a substantiallycircular path 148 in the region 118 of magnetic flux. Since thedirection of the repulsed electron is oppositeto the direction of themotion of the electrons incident to the plate member 134, the magneticfield in the region 118 acts to deflect the electrons to the right intoa non-reciprocal path 150. The electrons move to the right along thepath 150 until they enter the magnetic field produced within theshielding element 102 by the magnetic coil 122. This field, which hasits lines of flux substantially perpendicular to the velocity of theelectron beam, deflects its electrons along substantially circular paths152 into an undeflected path 154 which can be aligned with or madesubstantially parallel to the direction of the beam of electrons 94 asemitted by the electron gun 92.

When the beam of electrons along the path 152 emerges from the region156, its path 154 forms an angle with the boundary of the magnetic fieldwhich operates to narrow or sharpen the beam providing a cross sectionwhich is substantially similar to that of the original beam 94 emergingfrom the electron gun 92.

In the tube device 82 each of the magnetic fields produced by the magnet112, and magnetic coils 120, 122 may have a magnetic field intensity ofapproximately 50 gausses to provide the required deflection of the beamof Thus, the electron tube device 82 may be used as an amplifying deviceby delivering an input signal to the lead 136 of the plate member 134which in turn modulates the intensity of the beam of electrons whichelectrons are delivered to the collector plate 128 producing an outputsignal. The tube device, in this manner, may be used for voltage orcurrent amplification.

As previously noted many advantages are provided by this structurebecause of the low input capacitance and high transconductance achievedby the device. The device also provides high efliciency with low powerdissipation, high reliability and long tube life.

Instead of providing a collector plate 128, the device 82 may beprovided with focusing and deflecting means and a fluorescent screen toform an in line type of cathode ray tube instead of the bent cathode raytube 10 shown in FIGURE 1. Of course the modulated beam produced by thedevice may be utilized to form many other electronic devices having manyif not all of the enumerated advantages.

The invention may be adapted to utilize charged partioles other thanelectrons embodying the basic features disclosed herein. For example,the method of the invention may be applied by subjecting a chargedparticle or a beam of charged particles to a magnetic field fordeflecting the particles along a predetermined path into an electricvector field, varying the vector intensity of the electric field forcontrolling the proportion of particles rejected by the electric field,and forming the electrons rejected by the electric field into a beam ofparticles. The beam of rejected particles may also be further deflectedby a magnetic field into a desired non-reciprocal path. The intensityvector of the electric field is directed parallel to the path of theparticles for reflecting or rejecting the panticles from the electricfield along a path substantially identical in direction to the path ofthe incident particles. The method of the invention, it will be noted,may readily be applied to removing or absorbing particles for modulatingthe intensity of the beam comprising positively or negatively chargedparticles having a mass greater or smaller than that of the electron.

Refer to FIGURES 4 and 5 which shows a signal combining means 160comprising a substantially cylindrical glass envelope 16-2 having acylindrical wall 164 and top and bottom walls 166, 168. The envelope 162has its chamber evacuated and sealed in the usual manner.

A cylindrical shielding element 170 is positioned by a plurality ofradially extending spacing means 172 within the envelope 162 with itsaxis aligned with the axis of the envelope 162. The spacing means may bein the form of springs to adjust for relative expansion and contractionof the envelope 162 and shielding element 170. The spacing means 172also provides a peripherial annular region 174 between the side wall 164of the envelope 162 and the shielding element 170. A cathode 176 ispositioned within the annular region 174, and is associated with aheating element 178. The cathode 176 may be returned to ground potentialwhile the heating element 178 may be energized by an appropriate currentsource.

A plurality of plate members 180, 182, and an electron collecting plate184 are angularly positioned in spaced relationship within the annularregion 174 of the envelope 162. The members 180 and 182 may be oined torespective external terminals 186, 188 which are each adapted to receiveinput signals, while the collector plate 184 is connected to an externallead 190' which is joined to a terminal 192 maintained at an appropriatepotential through a load 194. A lead 195 connects the shielding element170 to a terminal 197 for being maintained at an appropriate voltagewhich is positive with respect to the cathode 176. For example, thedevice may be operated with a positive potential of 100 to 500 volts on11 6 te minal 197 of the shielding element 170.

The shielding element is provided with a plurality of apertures 196,198, 200 and 2.02 each respectively positioned proximate the cathode176, plate members 180, 182 and the collector plate 184.

A substantially uniform magnetic field is produced in the region 204inside the shielding element 170. The lines of flux of the magneticfield are parallel to the cylindrical axis of the shielding element 170and perpendicular to the plane of FIGURE 5. The magnetic field isproduced by a magnet 206 having the faces of its poles 208, 210respectively parallel and proximate to the top and bottom walls 166, 168of the envelope 162.

In operation, the electrons emitted by the heated cathode 176 areaccelerated towards the shielding element 170 because of its higherpotential. T he'elect'rons which pass through the aperture 196 in theelement 178 form a beam of electrons 212 which are deflected into asubstantially curved path 214 by the magnetic field within the region204. The path 214 is substantially circular since the velocities of theelectrons are perpendicular to the lines of magnetic flux. The electronsalong the path 214 pass through the aperture 198 of the shieldingelement 170 towards the plate member 180 in a direction perpendicular toits electron intercepting surface.

As previously explained in connection with the devices 10 and 82 theelectric field produced between the shielding element 170 and the platemember 180 acts upon the electrons to decelerate them. As the modulatingsignal delivered to the terminal 186 varies the potential of the platemember 180 about substantially ground potential, the proportion ofelectrons repelled and not absorbed by the member 180 is correspondinglycontrolled. The repelled or reflected electrons, like the incidentelectrons, move substantially parallel to the lines of force of theelectric field and pass back through the aperture 198 forming a beam 216with a modulated amplitude within the region 204 of the device 160.

The magnetic field within the region 2% acts upon the beam 216 todeflect the electrons along a non-reciprocal substantially circular path218 which proceeds to the right and causes the electrons to pass throughthe aperture 200 into the electric field between the shielding element170 and the plate member 182. As before the variation of potential ofthe plate member 182 by the application of an input signal to itsterminal 188 varies the electric field acting upon the electrons. Inthis manner, the ratio of electrons which are absorbed to thosereflected is controlled. The reflected electrons pass back through theaperture 200 forming a beam of electrons 220 in the magnetic field ofthe central region 204 of the device 160. The beam 220, however, has anamplitude which is further modulated by the signal delivered to theterminal 188.

The beam 220 is deflected by the magnetic field along a non-reciprocalcircular path 222 and through the aperture 202 toward the collectorplate 184. Since the collector plate 184 is maintained at a potentialwhich is substantially above ground potential, it absorbs substantiallyall of the electrons of the beam 220. This produces an output signalacross the load 194. The output signal produced is related to theamplitude of the beam 220 which has been appropriately modulated by theseveral input signal delivered to the terminals 186 and 188.

Although the device 160 has been described with two plate members, manysuch members may be arranged within the annular region 174 for combininga plurality of input signals. In order to reduce the magnetic fieldnecessary to sharply deflect the beam of electrons, the plate membersmay be spaced about the periphery so that the beam passes from one platemember to a non-adjacent plate member and makes more than one revolutionabout the central region 204 before it impinges upon the collectorplate. By this means a highly compact signal combining device may beprovided which is adapted to receive a plurality of signals.

As noted in connection with the devices and 82, the signal combiningdevice 160 has a low input signal capacitance and provides goodinsulation between input electrodes while using one magnetic field forparticle deflection. Such devices can be especially useful in conreceivea plurality of input signals.

The FIGURE 6 is a diagrammatic view of a klystron device 224 embodyingthe invention. The device 224 comprises a tubular envelope 226 having afirst end 223 and a second 230. The first end 228 of the device 224 issubstantially similar to the beam modulating device 82 of FIGURE 2except that the distance between the shielding element 102 and thecollector plate 231 is greatly enlarged.

The second end 230 of the envelope 226 is provided with a pair of spacedresonating units 232, 234 having their central portions 236, 238extending into the envelope 226 forming respective apertures 240, 242along the linear path of the beam of electrons. The resonating units232, 234 are of the usual type made of a conducting material and havingannular cavity regions 244. The resonating unit 232 which precedes theunit 234 along the beam of electrons is connected to a terminal 246 forreceiving input signals which may be of radio frequency, while theresonating unit 234 is connected to a terminal 248 for delivering anoutput signal.

In operation, the beam produced by the device 224 is modulated by theinput signal delivered to the terminal 136 of the plate member 134. Thisbeam which has its amplitude modulated passes through the opening 240 ofthe resonating unit 232 which accelerates and decelerates the electronsin accordance with the input signal delivered to its terminal 246. Whenthe beam of electrons pass through the opening 242 of the resonatingunit 234 they induce an appropriate signal therein which is delivered toterminal 248. This output signal, thus, is modulated by the inputsignals to the terminals 136 and 246. The electrons which emerge fromthe opening 242 impinge upon and are removed by the collector plate 231which is returned to a positive potential.

The device 224 provides a beam of electrons which is not defocused bythe modulating input signals and has the further advantage of beingdriven by a small input signal voltage and requiring low power. Theconstruction also reduces the noise output which would be produced bypartition noise caused by collisions of the electrons of the beam withelectrodes in the beam path.

Although the above devices illustrate some of the forms of the inventionand some of its uses, the invention may be utilized in other devicessuch as backward traveling wave tube as well as various other forms ofamplifiers and signal generating and combining means.

While only a few representative embodiments and methods of practicingthe invention disclosed herein, have been outlined in detail, there willbe obvious to those skilled in the art, many modifications andvariations accomplishing the foregoing objects and realizing many or allof the advantages, but which yet do not depart essentially from thespirit of the invention.

What is claimed is:

1. A system for modulating the intensity of a beam of electricallycharged particles, said system comprising: means for projecting saidbeam along a predetermined path; means for magnetically deflecting saidbeam into a different path at an angle to said predetermined path; andmeans for reflecting along a reciprocal of said different path afraction of the particles in said beam while absorbing the remainder ofsaid particles.

2. The system of claim 1 further characterized in that said reflectingmeans comprises means for establishing in said different path anelectric field having lines of force parallel to said last-named pathand of such polarity as to retard particles entering said electric fieldfrom the direction of said magnetic field.

3. The system of claim 2 further characterized in that said means forprojecting said beam comprises an electric accelerating field ofpredetermined strength, said system further comprising means for varyingthe strength of said retarding electric field over a range of valuesextending both above and below that of said accelerating electric field.

4. A system for modulating the intensity of a beam of electricallycharged particles, said system comprising: an electrode for emittingsaid particles; means for forming said particles into said beam andprojecting said beam along a predetermined path; means for establishinga magnetic field transversely to said path whereby said beam isdeflected into a different path; and means for reflecting back into saidfield along a reciprocal of said dilferent path a controllable fractionof the particles in said beam while absorbing the remainder, saidlast-named means comprising an electrode disposed in said different pathand means for varying the potential of said electrode over a range ofvalues extending both above and below the potential of said emittingelectrode.

5. The system of claim 4 further comprising an electrode for shieldingsaid electrode of variable potential from other electrodes affectingsaid beam.

6. The system of claim 4 further comprising means for increasing thecross-section of said projected beam before traversal of said magneticfield.

7. The system of claim 6 further comprising means for reducing thecross-section of said reflected beam after traversal of said magneticfield.

References Cited in the file of this patent UNITED STATES PATENTS2,159,534 Ruska May 23, 1939 2,205,071 Skellett June 18, 1940 2,332,876Uhlmann Oct. 26, 1943 2,416,302 Goodall Feb. 25, 1947 2,416,303 ParkerFeb. 25, 1947 2,452,075 Smith Oct. 26, 1948 2,460,402 Sziklai Feb. 1,1949 2,651,000 Linder Sept. 1, 1953 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,023,342 February 27, 1962 GlennW. Preston that error appears in the above numbered pat- It is herebycertified that the said Letters Patent should read as ent requiringcorrection and corrected below.

lines 47 and 48, for "transductance" read Column 1, transconductancecolumn 8, line 75, after "of" insert input column 9 line 6, for "receivea plurality of read nection with electric computers input signals Signedand sealed this 2nd day of April 1963.

(SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting ()fficer Commissioner ofPatents

